However, in many real-world collisions, we perceive momentum as not being conserved because:
* External forces: The most common reason is the presence of external forces acting on the colliding objects. For example:
* Friction: Friction between the colliding objects and the surface they are on can dissipate energy and reduce the total momentum of the system.
* Air resistance: Air resistance can also act as a force, changing the momentum of objects in flight.
* Gravity: If the collision occurs over a significant distance, gravity can influence the motion of the objects, affecting momentum.
* Internal forces: Collisions often involve internal forces, like the forces generated within the objects themselves during deformation. These forces can transfer momentum to parts of the system not initially involved, making it appear as if momentum is lost.
* Non-elastic collisions: In non-elastic collisions, some kinetic energy is converted into other forms of energy, like heat, sound, or deformation. While the total energy of the system is conserved, the change in kinetic energy can make it seem like momentum is not conserved.
Example: A car crashing into a wall is not a closed system. The force of the wall, friction between the tires and the road, and the deformation of the car all act as external forces that influence the momentum of the system.
Key point: Even though we may not always observe the conservation of momentum in real-world collisions, it is a fundamental law of physics that always applies in a closed system.
